In order to use the Pythagorean theorem to find the magnitude of a resultant vector, which must be true regarding the two initial vectors?

The Pythagorean theorem applies to a right triangle. When the two initial vectors are perpendicular, they form a 90-degree angle, and their magnitudes are the legs of the triangle; the resultant is the hypotenuse. Therefore, the vectors must form a 90-degree angle.

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